Part Number: DS560MB410
Dear TI Team,
We are currently evaluating PAM4 signal quality using the DS560MB410 linear redriver.
The DS560MB410 output is being measured using a Keysight UXR0204B oscilloscope, and PAM4 Eye metrics and RLM are being evaluated.
During our evaluation, we have observed the following behavior.
Observation
In the PAM4 eye diagram,
- Upper Eye (+3 ↔ +1)
- Center Eye (+1 ↔ −1)
- Lower Eye (−1 ↔ −3)
the center eye opening is sometimes significantly smaller than the upper and lower eyes.
In the DS560MB410 Programmer's Guide, the Eye Expander section states:
"PAM4 outer eye compression occurs..."
"Eye Expander may be used to improve PAM4 signal symmetry and balance the PAM4 signaling levels." [SNLU286_DS...nfidential | PDF]
However, we could not find guidance describing the mechanism behind center-eye compression or its relationship to CTLE and Eye Expander settings.
We would appreciate clarification on the following points.
Questions
1.
Can DS560MB410 CTLE settings contribute to reduced PAM4 center-eye opening?
2.
Have you observed cases where increasing CTLE Boost improves the internal Eye Height Monitor reading, while causing degradation in:
- PAM4 linearity
- RLM
- Center-eye opening
?
3.
Is the Eye Expander primarily intended to improve:
- Center Eye
- Upper Eye
- Lower Eye
or all PAM4 eye openings equally?
4.
Is center-eye compression typically correlated with any of the following?
- CTLE Boost setting
- Eye Expander setting
- Driver output level (VOD)
- Input differential amplitude (VID)
- Driver linearity limits
- PAM4 level linearity (RLM)
5.
Does TI have a recommended methodology for selecting CTLE settings in PAM4 applications using:
- Center Eye opening
- Outer Eye opening
- RLM
?
Any supporting application note, characterization report, or design guide would be greatly appreciated.
6.
If center-eye compression is observed at the DS560MB410 output, what troubleshooting flow does TI recommend?
For example:
- CTLE adjustment
- Eye Expander adjustment
- VOD tuning
- Input amplitude optimization
Thank you for your support.
Best regards